liner

**Liner** is a **thin conductive film deposited inside a via or trench after the barrier** — providing adhesion between the barrier metal and the copper fill, promoting good wetting for electroplating, and enhancing electromigration resistance. **What Is a Liner?** - **Material**: Tantalum (Ta, BCC α-phase preferred for Cu adhesion), Cobalt (Co), or Ruthenium (Ru). - **Function**: - **Adhesion**: Cu does not stick well to TaN. The Ta liner provides the "glue." - **Wetting**: Promotes uniform Cu seed deposition and void-free electroplating fill. - **EM Resistance**: A strong Cu/liner interface resists electromigration mass transport. - **Thickness**: 1-3 nm (scaled aggressively at advanced nodes). **Why It Matters** - **Void-Free Fill**: Without a proper liner, Cu electroplating produces voids and seams that cause open failures. - **Reliability**: The Cu/liner interface is the critical path for electromigration lifetime. A weak interface = early failure. - **New Materials**: Co and Ru liners at 7nm and below improve fill and EM but add process complexity. **Liner** is **the adhesive layer for copper wires** — ensuring the metal fills cleanly and stays firmly bonded for the lifetime of the chip.